Abnormal function of NMDA receptor has been suggested to be correlated with the pathogenesis of Parkinson's disease (PD) as well as with the development of L-3,4-dihydroxyphenylalanine (L-DOPA)-induced dyskinesia. Here we show that NMDA receptor NR2 subunits display specific alterations of their subcellular distribution in striata from unilateral 6-hydroxydopamine-lesioned, L-DOPA-treated dyskinetic, and L-DOPA-treated nondyskinetic rats. Dyskinetic animals have significantly higher levels of NR2A subunit in the postsynaptic compartment than all other experimental groups, whereas NR2B subunit shows a significant reduction in both dopaminedenervated and dyskinetic rats. These events are paralleled by profound modifications of NMDA receptor NR2B subunit association with interacting elements, i.e., members of the membrane-associated guanylate kinase (MAGUK) protein family postsynaptic density-95, synapse-associated protein-97 and synapse-associated protein-102. Treatment of nondyskinetic animals with a synthetic peptide (TAT2B) able to affect NR2B binding to MAGUK proteins as well as synaptic localization of this subunit in nondyskinetic rats was sufficient to induce a shift of treated rats toward a dyskinetic motor behavior. These data indicate abnormal NR2B redistribution between synaptic and extrasynaptic membranes as an important molecular disturbance of the glutamatergic synapse involved in L-DOPA-induced dyskinesia.

Activation of dopamine D 1 receptors is critical for the generation of glutamate-induced long-term potentiation at corticostriatal synapses. In this study, we report that, in striatal neurons, D 1 receptors are co-localized with N-methyl-D-aspartate (NMDA) receptors in the postsynaptic density and that they co-immunoprecipitate with NMDA receptor subunits from postsynaptic density preparations. Using modified bioluminescence resonance energy transfer, we demonstrate that D 1 and NMDA receptor clustering reflects the existence of direct interactions. The tagged D 1 receptor and NR1 subunit cotransfected in COS-7 cells generated a significant bioluminescence resonance energy transfer signal that was insensitive to agonist stimulation and that did not change in the presence of the NR2B subunit, suggesting that the D 1 receptor constitutively and selectively interacts with the NR1 subunit of the NMDA channel. Oligomerization with the NR1 subunit substantially modified D 1 receptor trafficking. In individually transfected HEK293 cells, NR1 was localized in the endoplasmic reticulum, whereas the D 1 receptor was targeted to the plasma membrane. In cotransfected cells, both the D 1 receptor and NR1 subunit were retained in cytoplasmic compartments. In the presence of the NR2B subunit, the NR1-D 1 receptor complex was translocated to the plasma membrane. These data suggest that D 1 and NMDA receptors are assembled within intracellular compartments as constitutive heteromeric complexes that are delivered to functional sites. Coexpression with NR1 and NR2B subunits also abolished agonist-induced D 1 receptor cytoplasmic sequestration, indicating that oligomerization with the NMDA receptor could represent a novel regulatory mechanism modulating D 1 receptor desensitization and cellular trafficking. Dopaminergic fibers originating in the substantia nigra and cortical glutamatergic neurons extensively interact in the striatum to drive the physiological functions of this structure from motor planning to reward seeking and procedural learning (1, 2). The critical importance of dopamine in this system is such that the degeneration of nigral dopaminergic neurons leads to the motor and cognitive deficits of Parkinson's disease (3).At the cellular level, nigral and cortical fibers converge on the medium spiny projection neurons (4), where dopamine D 1 -and D 2 -like receptors are coexpressed to high degree with glutamate NMDA 1 and non-NMDA receptor channels (5-8). From a functional point of view, it is well established that dopamine modulates the firing pattern of these neurons. In particular, there is evidence that dopamine, while attenuating the responses mediated by non-NMDA receptors, potentiates those associated with activation of NMDA receptors (2). The D 1 receptor appears to be involved in these interactions. In fact, activation of D 1 receptors in medium spiny neurons enhances NMDA-induced whole cell currents (2, 9) and is a critical requirement for the formation of NMDA-mediated long-term potentiation at corticostriatal...

ABSTRACT:It has been recently demonstrated that the 43-kDa transactive response (TAR)-DNAbinding protein (TARDBP) is the neuropathological hallmark of Frontotemporal Dementia (FTD) with ubiquitin-positive and tau-negative inclusions. Large series of FTD patients without motor neuron disease have been previously analysed, but no TARDBP mutation was identified. The aim of the present study was to evaluate whether TARDBP gene mutations may be associated with FTD. We report that a pathogenetic TARDBP mutation is causative of behavioural variant FTD (bvFTD). An aged woman in her seventies initially started to present apathy and depression associated with impairment in executive functions. The diagnosis of bvFTD (apathetic syndrome) was accomplished by three-year follow-up, and structural and functional neuroimaging. By fiveyears after onset, extensive electrophysiological investigations excluded subclinical motor neuron disease. In this patient, a single base substitution c.800A>G of TARDBP gene was identified. This mutation, already described as causative of ALS, predicted the amino acidic change arginine to serine at position 267 (N267S). In silico analysis demonstrated that this substitution generates a new phosphorylation site, and western blot analysis on lymphoblastoid cells reported a decrease of protein expression in N267S mutation carrier. Our study suggests that TARDBP mutations can be pathogenetic of bvFTD without motor neuron disease. TARDBP screening needs to be considered in FTD cases.

Alzheimer's disease (AD) is a chronic neurodegenerative disorder caused by a combination of events impairing normal neuronal function. Here we found a molecular bridge between key elements of primary and secondary pathogenic events in AD, namely the elements of the amyloid cascade and synaptic dysfunction associated with the glutamatergic system. In fact, we report that synapse-associated protein-97 (SAP97), a protein involved in dynamic trafficking of proteins to the excitatory synapse, is responsible for driving ADAM10 (a disintegrin and metalloproteinase 10, the most accredited candidate for ␣-secretase) to the postsynaptic membrane, by a direct interaction through its Src homology 3 domain. NMDA receptor activation mediates this event and positively modulates ␣-secretase activity. Furthermore, perturbing ADAM10/SAP97 association in vivo by cell-permeable peptides impairs ADAM10 localization in postsynaptic membranes and consequently decreases the physiological amyloid precursor protein (APP) metabolism. Our findings indicate that glutamatergic synapse activation through NMDA receptor promotes the non-amyloidogenic APP cleavage, strengthening the correlation between APP metabolism and synaptic plasticity.

A correct interplay between dopamine (DA) and glutamate is essential for corticostriatal synaptic plasticity and motor activity. In an experimental model of Parkinson's disease (PD) obtained in rats, the complete depletion of striatal DA, mimicking advanced stages of the disease, results in the loss of both forms of striatal plasticity: long-term potentiation (LTP) and long-term depression (LTD). However, early PD stages are characterized by an incomplete reduction in striatal DA levels. The mechanism by which this incomplete reduction in DA level affects striatal synaptic plasticity and glutamatergic synapses is unknown. Here we present a model of early PD in which a partial denervation, causing mild motor deficits, selectively affects NMDA-dependent LTP but not LTD and dramatically alters NMDA receptor composition in the postsynaptic density. Our findings show that DA decrease influences corticostriatal synaptic plasticity depending on the level of depletion. The use of the TAT2A cell-permeable peptide, as an innovative therapeutic strategy in early PD, rescues physiological NMDA receptor composition, synaptic plasticity, and motor behavior.